Q. I have heard you mention applying fertilizer to trees and shrubs in the fall rather than the spring. Is now the right time to do that?
A. The concept is called “late fall fertilization”. I have mentioned it before. It first came to light in the management of lawn grasses. It was found the “effects” from applied nitrogen fertilizers in late fall could be stored over the winter. In the spring, these effects would “kick in” and get the lawn off to an early start without fertilizer applied in the spring.
This concept was applied to landscape plants. The same seems to hold true. If high nitrogen fertilizers are applied late in the fall the effects from nitrogen fertilizers can be delayed until the following spring. This must be done after growth has stopped in the fall but before leaf drop or even change in leaf color. This concept can be applied fruit trees as well.
|Too late for fall fertilization|
Outside of being a novelty, why would this be considered? Why not just apply the fertilizers in the spring? The primary reason, commercially, is labor. Frequently, springtime is a very labor-intensive time of the year for professionals. Late fall months, before pruning begins, is usually a slow time of the year. Taking a spring operation and moving it to the fall redistributes labor. Saves money for landscape companies. Maybe it is a better time for homeowners who do it themselves. Nice cocktail talk. Bragging rights.
|The lawn on the right was fertilized in the late fall. The one on the left was not. In Salt Lake City, Utah. Bluegrass mix.|
Timing is critical. Time late fall fertilization to a time when growth has stopped or nearly stopped but before leaves have begun losing their color. Plants should no longer be growing but the leaves should still pull water from the soil to distribute the fertilizer throughout the plant for storage. Avoid late fall fertilizing on winter tender plants that are woody such as citrus, bougainvillea and Cape honeysuckle.